1. Field of the Invention
This invention is related to the preparation of dynamic scattering liquid crystal display devices in general and more particularly to the preparation of reflective mode dynamic scattering liquid crystal display devices which operate under dc excitation.
2. Prior Art
A good dynamic scattering liquid crystal display device requires high contrast ratio and long operational life. For a reflective display, high reflectivity of a mirror-like surface and good scattering of liquid crystal are needed for high contrast ratios. Reflection mode, as opposed to transmission mode, dynamic scattering liquid crystal (LC) displays take maximum advantage of the ambient light to produce contrast.
Prior to this invention, reflective mode dynamic scattering displays were practically restricted to ac operations for two reasons: (1) the liquid crystal and/or the liquid crystal dopants were not stable under dc excitation and (2) many of the high reflectivity metals are either not stable themselves or cause the rapid degradation of an otherwise stable dc liquid crystal dopant system.
DC operation is a desirable characteristic because it reduces the complexity of the associated addressing circuitry, especially in the case of integrated circuits. High reflectivity electrodes have been known to be desirable for some time.
Aluminum, which is usually coated with a thin transparent coating of silicon dioxide has been used in the manufacture of liquid crystal displays that were strictly restricted to ac operation. A high contrast reflective type dynamic scattering display with long life under dc operations, however, was not previously available.
It is therefore an objective of this invention to provide a display device which exhibits high contrast ratio for long operating periods.
A second objective of this invention is to provide a reflective mode dynamic scattering liquid crystal display device.
A third, and still further, objective of this invention is to provide a dynamic scattering liquid crystal display device that exhibits long operational life under dc mode excitation.
Applicants know of no prior art which meet all of their above stated objectives.